We established the assay conditions for human testicular FSH receptors using testicular tissues obtained from ten patients with prostate cancer. Based on the results of the time course study on specific FSH binding with increasing concentrations of the testicular homogenate at various temperatures, we found that the incubation was suitable at 25 degrees C for 20 hours using 10 mg wet tissue per tube. Scatchard analysis of specific FSH binding sites showed that FSH receptors in the human testicular tissue consisted of two classes of binding sites, one with a high affinity (Ka, 10(9) M-1) and the other with a low affinity (Ka, 10(8) M-1).